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Some years ago I was lucky enough to live in a house with a professional cook from Sweden. She cooked sauteed mushrooms used an interesting combination of fresh herbs -- half and half tansy and lemon balm, chopped -- to eat as mushrooms-on-toast or as side dishes with steak, roast beef or roast chicken. She called the mixture "balsam and tansy" but the "balsam" was definitely lemon balm.

The flavour was very interesting -- a mildly resinous citrus taste -- but I’ve never come across this combination anywhere else. I’d like to cook this dish again but notice that Richters sells tansy only for non-culinary uses. I’ve also have come across contradictory information at various places on the Internet suggesting there’s some doubt about whether tansy is safe to eat.

Do you have an opinion, and if you believe it’s edible, which variety of tansy would you recommend?

Actually, Richters does indicate that tansy is used for culinary purposes, in both the online and printed catalogues.

There are quite a number of herbs like tansy that have interesting culinary purposes but come with potential dangers if misused. Most observers take one look at the dangers of tansy oil and immediately assume that the plant is too dangerous to use in cooking. According to Dr. Jim Duke, in his "Handbook of Medicinal Herbs" (CRC Press, Boca Raton, FL), ten drops of the oil can be lethal!

But we know from long experience with herbs and spices that pure essential oils are often far more irritating and even surprisingly dangerous compared to the source herb itself. That’s because the extraction process concentrates the oil to levels far in excess of levels found naturally in plants. So, for example, oregano essential oil is highly irritating and must be used in moderation, even though the leaves are one of the most widely used herbs on the planet with a long history of safe use. There are many similar examples that I could tell you about from among the common everyday herbs and spices.

That being said, there are specific concerns about tansy that suggest caution is warranted. In sensitive individuals it can cause contact dermatitis, probably due to chemicals called allergenic sesquiterpene lactones that are found in it. The effect is not serious generally if the amount of herb taken is small, but it is something to watch for.

Of the fresh or dried herb (not the oil), Dr. Duke rates tansy as "dangerous as coffee" and that he "wouldn’t be afraid to drink two cups of it containing 10g of herb steeped." Duke has this to say about the herb’s culinary uses: "Although poisonous, tansy finds its way into omelets, puddings, and herbal teas. Fresh tender young leaves are used sparingly as a spice to flavor an omelet, a baked fish, or in meat pie."

According to the "Plants of the Future Database" (http://www.ibiblio.org/pfaf/cgi-bin/arr_html?Tanacetum+vulgare&CAN=LATIND), the herb is poisonous if ingested in large quantities. In North America, there have been deaths from the misguided consumption of overly strong brews of the tea to induce abortions.

What can we conclude from the above? If you decide to use tansy as a seasoning in food, use the fresh or dried herb sparingly, and never use the oil. How much fresh or dried herb can you use? It is hard say based on the available information, but probably 2-3 leaves in a dish that serves four should be okay for people who tolerate tansy well. Be on close watch for any sign of irritation of the skin, the mouth, or the digestive system, and stop serving foods with tansy to individuals who experience irritation. And finally, use tansy only occasionally, no more than, say, once or twice a month.